Some medical tests involve staining individual samples. The samples may be, for example, small pieces of tissue obtained from a subject by way of a biopsy. It is tedious and time consuming to manually stain individual samples. Manually staining individual samples also introduces the possibility of errors.
Conventional staining protocols involve batch staining by incubating volumes of pre-treatment reagent and primary reagents over an array of samples arranged on a slide. The reagents may include antibodies, immunohistochemical staining materials, other markers, or the like. Relatively large volumes of reagents can be required to ensure that all of the samples on a slide are appropriately treated. Reagents can be expensive. Consequently, batch staining is costly and can also compromise the accuracy of results. In addition, batch staining generally requires all of the samples on a slide to be treated with the same reagent(s).
There exist various devices for automatically dispensing reagents. These devices are typically not capable of reliably dispensing sub-microliter quantities of reagent. U.S. Pat. No. 5,143,849 discloses a method for automatically positioning a dispensing tip at a desired distance from a surface onto which liquid is to be dispensed. The method features the formation on the tip of a meniscus of a nominal small volume and advancing the tip and meniscus until the surface is contacted. The resulting decrease in pressure in the tip is measured, to trigger the tip to stop its advance and to start dispensing.
Some existing apparatus for depositing reagents onto samples cannot effectively deliver reagents through liquid coverslip layers that can be used to prevent dessication of samples.
There is a need for efficient and cost effective methods and apparatus for applying reagents to samples in the medical testing field and in other fields.